Bump platform

Signed-off-by: Louis Chemineau <louis@chmn.me>

composer.json

@@ -11,7 +11,7 @@
   ],
   "config": {
     "platform": {
-      "php": "7.4"
+      "php": "8.1"
     },
     "optimize-autoloader": true,
     "classmap-authoritative": true,
@@ -49,4 +49,4 @@
       "url": "https://git.friendi.ca/friendica/php-json-ld"
     }
   ]
-}
+}